The present invention relates to a refrigerant cycle in which a refrigerant circuit is constituted by sequentially connecting a compressor, a gas cooler, throttling means and an evaporator.
In this type of conventional refrigerant cycle apparatus, a refrigerant cycle (refrigerant circuit) is constituted by sequentially annularly pipe-connecting a compressor, e.g., a multistage compression type rotary compressor having an internal intermediate pressure, a gas cooler, throttling means (expansion valve or the like), an evaporator and others. Further, a refrigerant gas is taken into a low-pressure chamber side of a cylinder from an intake port of a rotary compression element of the rotary compressor, and compression is performed by operations of a roller and a vane, thereby obtaining a refrigerant gas having a high temperature and a high pressure. This refrigerant gas is discharged from a high-pressure chamber side to a gas cooler through a discharge port and a discharge sound absorbing chamber. The refrigerant gas releases its heat in the gas cooler, and is then throttled by the throttling means and supplied to the evaporator. The refrigerant is evaporated there and endotherm is performed from the circumference at this time, thereby demonstrating a cooling effect.
Here, in order to cope with the global environmental problems in recent years, there has been developed an apparatus using a transcritical refrigerant cycle which utilizes carbon dioxide (CO2) being a natural refrigerant as a refrigerant in place of conventional fluorocarbon and operates with a high-pressure side being used as a supercritical pressure.
In such a refrigerant cycle apparatus, in order to prevent a liquid refrigerant from returning into the compressor which results in liquid compression, an accumulator is arranged on a low-pressure side between an outlet side of the evaporator and an intake side of the compressor, the liquid refrigerant is stored in this accumulator, and only the gas is taken into the compressor. Furthermore, throttling means is adjusted so as to prevent the liquid refrigerant in the accumulator from returning into the compressor (see, e.g., Japanese Patent Application Laid-open No. 7-18602).
However, providing the accumulator on the low-pressure side of the refrigerant cycle requires a large refrigerant filling quantity. Moreover, an opening of the throttling means must be reduced or a capacity of the accumulator must be increased in order to avoid the return of the liquid, which leads to a reduction in cooling capability or an increase in installation space. Thus, in order to solve the liquid compression in the compressor without providing the accumulator, an applicant attempted a development of a refrigerant cycle apparatus depicted in a prior art drawing of FIG. 3.
In FIG. 3, reference numeral 10 denotes an internal intermediate-pressure multistage compression type rotary compressor, and this compressor comprises an electric element 14 in a sealed container 12, and a first rotary compression element 32 and a second rotary compression element 34 which are driven by a rotary shaft 16 of this electric element 14.
An operation of the refrigerant cycle apparatus in this example will now be described. A refrigerant with a low pressure sucked from a refrigerant introducing tube 94 of the compressor 10 is compressed to have an intermediate pressure by the first rotary compression element 32, and discharged into the sealed container 12. Thereafter, it flows out from the refrigerant introducing tube 92 and enters an intermediate cooling circuit 150A. The intermediate cooling circuit 150A is provided so as to run through a gas cooler 154, and heat of the refrigerant is released there by an air-cooling method. Here, heat of the refrigerant having an intermediate pressure is taken by the gas cooler.
Thereafter, the refrigerant is taken into the second rotary compression element 34 where the second compression is performed, and the refrigerant is turned into a refrigerant gas with a high temperature and a high pressure and discharged to the outside by a refrigerant discharge pipe 96. At this moment, the refrigerant is compressed to an appropriate supercritical pressure.
The refrigerant gas discharged from the refrigerant discharge tube 96 flows into the gas cooler 154 where heat of the refrigerant gas is released by the air-cooling method, and it passes through an internal heat exchanger 160. Heat of the refrigerant is taken by the refrigerant on a low-pressure side which has flowed out from an evaporator 157, and the former refrigerant is further cooled. Then, the refrigerant is reduced in pressure by an expansion valve 156 and enters a gas/liquid mixed state in this process. Then, it flows into the evaporator 157 and evaporates. The refrigerant which has flowed from the evaporator 157 passes through the internal heat exchanger 160, and it takes heat from the refrigerant on the high-pressure side, thereby further being heated.
Then, the refrigerant heated in the internal heat exchanger 160 repeats the cycle in which it is sucked into the first rotary compression element 32 of the compressor 10 from the refrigerant introducing tube 94. In this manner, a degree of superheat can be taken by heating the refrigerant which has flowed out from the evaporator 157 with the refrigerant on the high-pressure side by the internal heat exchanger 160, the return of the liquid that the liquid refrigerant is sucked into the compressor 10 can be prevented without provided an accumulator or the like on the low-pressure side, and an inconvenience that the compressor 10 is damaged by the liquid compression can be avoided.
In such a refrigerant cycle apparatus, when the compressor 10 is stopped, the refrigerant with a high pressure flows into the sealed container 12 from a gap of the cylinder 38, and a high pressure and an intermediate pressure reach an equilibrium pressure and then reach the equilibrium pressure together with a low pressure. Therefore, it takes a considerable time for the pressures in the refrigerant circuit to become an equalized pressure.
In this case, if there is a difference between a high pressure and a low pressure of the rotary compression elements at the time of restart after the stop, the startability is deteriorated and a damage may be possibly generated.
Additionally, since the intermediate pressure in the sealed container first reaches the equilibrium pressure together with the pressure on the high-pressure side, the pressure is increased after stopping the normal operation. Therefore, the pressure proof design of the sealed container of the compressor must be carried out taking an increase in pressure after the stop into consideration, which results in an increase in production cost.